The organic EL devices have been expected to be applied to color wide screen image display devices replacing liquid crystal display devices, and have been intensively developed. Recently, although displays using the organic EL devices have now been used in practical applications, full-color image display devices using the same are still in the course of development because they lack in sufficient light emitting property. Very high efficiency green organic light emitting devices based on electrophosphorescence employing ortho metalized iridium complex (fac-tris(2-phenylpyridine)iridium) as a phosphorus light emitting material for improving properties of the organic EL device are proposed. (refer to, for example, D. F. O'Brien and M. A. Baldo et al “Improved energy transferring electrophosphorescent devices” Applied Physics letters Vol. 74 No. 3, pp 442-444, Jan. 18, 1999; and M. A. Baldo et al “Very high-efficiency green organic light emitting devices based on electrophosphorescence” Applied Physics letters Vol. 75 No. 1, pp 4-6, Jul. 5, 1999).
Because the current organic EL devices employing the phosphorus photoluminescence are limited to emitting only green light, coverage as the color display devices is narrow. Therefore, it has been demanded to develop organic EL devices which emit light of different colors from green with improved light emission property. Regarding particularly with EL devices which emit blue light, those having an external quantum yield exceeding 5% is not reported yet. Accordingly, an improvement in the EL devices which emit blue light, if possible, enables the display devices to display full colors or white light resultantly advancing toward practical use of phosphorus light EL device greatly.
Further, although International PCT Patent Publication No. WO 02/15645 discloses following structures of ligands (A) and (B):
wherein R1 to R5 each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aromatic group and an arylene group; and R1′ and R2′ an aromatic group, which may bond each other;any practical synthesis example of real complex with the use of the ligands is not described.